DESCRIPTION: The long-term objective of this research is to develop a new, general paradigm for construction of biosensors based on complexes between proteins and colloidal Au nanoparticles. This idea is founded on the hypothesis that appropriately-sized colloidal Au nanoparticles can be used as non-denaturing photon and electron antennae for proteins, allowing protein:Au colloid complexes to be used as building blocks for a variety of sensing mechanisms. To that end, the proposed work will demonstrate direct electrochemistry of enzyme:Au complexes. It will also show that antibody:Au complexes can be used to detect small-molecule antigens by surface enhanced Raman scattering (SERS), to improve the mass resolution in surface plasmon resonance spectroscopy, and to detect protein antigens by binding-induced changes in electrical resistance. Preliminary studies have already shown that: (i) reversible electrochemistry of cytochrome c is obtained at Au colloid-modified electrodes without any pretreatment; (ii) covalent attachment of Cc:Au complexes to roughened Ag surfaces facilitates acquisition of SERS spectra; (iii) electrically conductive surfaces can be prepared by Au colloid multilayer assembly; and (iv) Au particle size impacts SERS enhancement factors, electrochemical reversibility, and enzymatic activity. These data show that colloidal AU particles are unique in their ability to interact favorably with photons, electrons, and proteins, as well as to be assembled into well-defined, easily-characterized macroscopic surfaces.